The present invention relates to a method for nondestructively determining the nuclear spin distribution and the relaxation time distribution in an object by using the nuclear magnetic resonance, and in particular to a method for measuring these distributions at high speed.
A known method for determining the nuclear spin distribution in an object at high speed is the so-called echo-planar method described in Journal of Magnetic Resonance, 29, pp. 355-373, 1978 in detail. This method includes exciting the nuclear spins, applying a fixed field gradient to the spins in a direction, applying in a direction perpendicular to the above described direction a field gradient periodically inverted in sense, and measuring the nuclear spin signals while field gradients are applied to the object. Since the two-dimensional spin distribution is obtained by the measurement after one excitation attempt, the echo-planar method advantageously has a very short measurement time. However, the echo-planar method has a drawback that a gradient magnetic field having a large amplitude must be changed over at high speed to obtain an image having a quality of practical use.
In the chemical shift imaging method described in U.S. Patent Application "High Speed Imaging Method by Three-dimensional NMR" by the present inventors (filed on June 20, 1980), inversion of the gradient magnetic field similar to that of the echo-planar method is used. Accordingly, the chemical shift imaging method also has the above described problem.